Hi,
Please share us what machine you are using to open group policy objects editor.
Based on my test, user tab is only enabled on member servers or clients in domain, not on DC.
Also, please make sure that the account you are using has administrator permission to do this.
In addition, here is a similar thread which suggested to install kb313222 hotfix, you could take a look and use for reference:
https://social.technet.microsoft.com/Forums/windows/en-US/fdb24c66-9988-4bb8-9008-7bd25aa36c1b/users-tab-missing-in-windows-xp-group-policy-object-editor?forum=itproxpsp
Best Regards,
Wendy
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